The present invention relates to a reader and/or writer for performing transmission of proximity radio operating power to and communications with proximity radio cards such as a cash card, a credit card, a railway ticket, a commutation ticket, a coupon ticket, a management card, an ID card, a license, etc. employed in, for example, a cash dispenser, electronic money, an automatic checking and collecting system, a room in/out management system, etc.
It has heretofore been known in Japanese Patent Application Laid-Open Nos. Hei 7-85233 and 9-62816 that power is supplied to a proximity radio card (IC card) from the power supply side in a noncontact manner with the card by using light or magnetic fields.
In a noncontact card system (proximity radio card system) wherein when cash cards, credit cards, railway tickets, commutation tickets, etc. to be used at wickets in railway stations or on buses or at entrances and exits or the like are brought into IC cards, and when a user causes his/her IC card to pass through a reader and/or writer provided at a wicket in a railway station or on a bus or at an entrance and exit or the like in a noncontact manner with the reader and/or writer, a power transmitting wave or a communication wave is radiated from a coil or an antenna of the reader and/or writer and the electromagnetic wave is received by and thereby a voltage is induced by a coil or an antenna provided on the card side to thereby operate circuits on the card side, whereby a signal is detected, the electric field radiated from the coil or antenna of the reader and/or writer needs to satisfy the restricted value (500 .mu.V/m at a distance of 3 m) of the Wireless Telegraphy Act.
However, a problem arises in that since the upper limit of the value of a current flowing through the coil or antenna for the reader and/or writer is determined under the restricted value (500 .mu.V/m at the distance of 3 m) of the radiated electric field according to the Wireless Telegraphy Act and the upper limit of the intensity of a magnetic field necessary for power transmission and communications is determined according to the upper limit of the current value, a communicable range is restricted.
Japanese Patent Application Laid-open No. Hei 9-212606 as a prior art discloses a noncontact reader and/or writer having three or more loop coils wherein carrier signals, which are different in phase to each other, are applied at a predetermined frequency across each of the plurality of loop coils with a phase shifter to cancel electromagnetic fields at a distant so that effect upon radiation to peripheral devices is suppressed. In such a prior art, however, a waveform on which magnetic fields generated from each coil are overlapped is supplied to a card. As a result, the overlapped wavefom has a waveform width wider than that of a desired waveform, resulting in deformation. Thus, it is impossible to transmit correct information.